This is a very interesting article about vitamin B12 deficiency. Non experts, like me, generally know little about this vitamin and effects. Here is an extract of the article for your information:
A severe B12 deficiency results in anemia, which can be picked up by an ordinary blood test. But the less dramatic symptoms of a B12 deficiency may include muscle weakness, fatigue, shakiness, unsteady gait, incontinence, low blood pressure, depression and other mood disorders, and cognitive problems like poor memory.
Labs differ in what they consider normal, but most authorities say a deficiency occurs when B12 levels in adults fall below 250 picograms per milliliter of blood serum. Like all Bvitamins, B12 is water-soluble, but the body stores extra B12 in the liver and other tissues. Even if dietary sources are inadequate for some time, a serum deficiency may not show up for years.
If the amount of B12 in storage is low to begin with, a deficiency can develop within a year, even more quickly in infants.
Recommended dietary amounts of B12 vary: 2.4 micrograms daily for those age 14 and older, 2.6 micrograms for pregnant women and 2.8 micrograms for nursing women. Barring circumstances that impair B12 absorption, these are levels easily obtained from awell-balanced diet containing animal protein.
In its natural form, B12 is present in significant amounts only in animal foods, most prominently in liver (83 micrograms in a 3.5-ounce serving). Good food sources include other red meats, turkey, fish and shellfish. Lesser amounts of the vitamin are present in dairy products, eggs and chicken.